1. Field of the Invention
The present invention relates to a system for pumping a fluid medium from a lower level to a higher level, or from a lower pressure to a higher pressure.
2. The Prior Art
Fluid medium is caused to flow from one point to another or from one state to another usually by the use of pumps operating at substantially constant speeds, and control of the flow is usually achieved by the use of throttle valves connected in series with the pumps. Sometimes the throttle valves are instead located in flow lines arranged to run parallel to the constant-speed pump (via by-pass lines), and sometimes the pumps connected in series with the throttle valves may be operated by variable-speed controlled motors. From an overall energy efficiency point of view, only the latter-mentioned system is really acceptable. However, even with the latter-mentioned system, the higher the static lifting height, the smaller the relative energy savings are obtainable because even in the case of low volume flows the required pump effect is substantial. This effect sometimes even exceeds the required effect needed when the pump is operating at its nominal working mode. For low flows and high pressure heights, this means that it is never possible to reduce to zero the volume flow without making special arrangements with regard to cooling of the pump.
The present invention is directed to a pumping system which helps to obviate the energy losses incurred with prior art pumping systems, as well as other problems associated therewith, especially when operating at low fluid flow conditions.